This invention relates to systems and methods for aligning an optical device system with an optical lens system.
Many advanced communication systems transmit information through a plurality of parallel optical communication channels. The optical communication channels may be defined by a fiber optic ribbon interconnect (or fiber optic cable) formed from a bundle of glass or plastic fibers, each of which is capable of transmitting data independently of the other fibers. Relative to metal wire interconnects, optical fibers have a much greater bandwidth, they are less susceptible to interference, and they are much thinner and lighter. Because of these advantageous physical and data transmission properties, efforts have been made to integrate fiber optics into computer system designs. For example, in a local area network, fiber optics may be used to connect a plurality of local computers to centralized equipment, such as servers and printers. In this arrangement, each local computer has an optical transceiver for transmitting and receiving optical information. The optical transceiver may be mounted on a printed circuit board that supports one or more integrated circuits. Typically, each computer includes several printed circuit boards that are plugged into the sockets of a common backplane. The backplane may be active (i.e., it includes logic circuitry for performing computing functions) or it may be passive (i.e., it does not contain any logic circuitry). An external network fiber optic cable may be connected to the optical transceiver through a fiber optic connector that is coupled to the backplane.
Vetical cavity surface emitting lasers (VCSELs) are becoming an important element of fiber optic links in modern data communication. For example, VCSELs have replaced light-emitting diodes (LEDs) in all local area network (LAN) applications for data rates of 1 Gigabits-per-second (Gb/s) or higher. The rapid increase in Internet traffic is creating communications bottlenecks in the back plane of computers and in the switches and routers that direct the data flow throughout computer networks. Since these applications cover a relatively short distance (e.g., about 1-100 meters), it is more economical to use parallel links over multiple fibers rather than higher speed serial links over a single fiber. Of particular interest is an application with twelve channels operating at 2.5 Gb/s. For short distance applications in which the cost of twelve-fiber ribbon interconnects is relatively low, this parallel solution is less expensive than a serial channel operating at the combined data rate of 30 Gb/s. Ribbon interconnects with four fibers, eight fibers and sixteen fibers operating at data rates of 1-10 Gb/s per channel and with aggregate throughputs in excess of 100 Gb/s are expected to be developed within the next two years.
By design, a VCSEL emits laser light from the top surface of a light-emitting cavity with a relatively small beam divergence (e.g., on the order of 10xc2x0). These features allow VCSELs to be arranged in one-dimensional or two-dimensional arrays, tested in parallel, and easily incorporated into an optical transceiver module and coupled to a fiber optic ribbon interconnect. Efforts have been made to simplify the problem of aligning the optical ports of an optical transceiver module with the fibers of a fiber optic ribbon interconnect. In one single-fiber alignment approach, the optoelectronic device is die and wire bonded to a transceiver package so that it may be biased to its normal operating condition. The input end of the fiber is mechanically manipulated in front of the active region of the optoelectronic device until an optical coupling between the fiber and the optoelectronic device is achieved. After the optimal coupling has been achieved, the optoelectronic device is bonded in place. This process requires either human interaction or expensive equipment that automatically dithers the fiber into the optimal position. This conventional alignment process becomes significantly more complicated when applied to the coupling of arrays of optical fibers with arrays of optoelectronic devices. Additional difficulties arise when an optical lens system must be aligned between the optoelectronic devices and the optical fibers.
The invention features a scheme (systems and methods) for passively aligning one or more optical devices with a corresponding number of optical lenses in an accurate and efficient manner. By this approach, the invention avoids the often labor-intensive and costly steps required by conventional active alignment techniques that attempt to align the optical devices to the optical fibers.
In one aspect, the invention features an optoelectronic device, comprising an optical device system, an optical lens system and a plurality of solder bumps disposed therebetween. The optical device system includes an optical device substrate supporting one or more optical devices and a solderable metallization pattern having a spatial arrangement with respect to the one or more optical devices. The optical lens system includes one or more optical lenses and a device bonding surface supporting a solderable metallization pattern having a spatial arrangement with respect to the one or more optical lenses. The solder bumps are disposed between the metallization patterns of the optical device system and the optical lens system. The plurality of solder bumps bond the optical device substrate to the device bonding surface with the one or more optical devices aligned with the one or more optical lenses.
Embodiments in accordance with this aspect of the invention may include one or more of the following features.
The one or more optical lenses may be incorporated into the device bonding surface. Alternatively, the one or more optical lenses may be recessed below the device bonding surface.
In some embodiments, the optical lens system includes an optical substrate incorporating the one or more lenses and the device bonding surface defines one face of a spacer substrate. The optical substrate may be bonded to the spacer substrate by a wafer bonding process or a flip-chip solder bonding process. The thickness of the device bonding substrate preferably is selected based upon a representative focal distance between the one or more optical devices and the one or more optical lenses. The spacer substrate may be transparent or it may comprise one or more apertures through which light is transmitted between the one or more optical devices and the one or more optical lenses. An integrated circuit may be formed on the spacer substrate and may be configured to drive the one or more optical devices. Alternatively, the integrated circuit may be bonded to the spacer substrate by a flip-chip solder bonding process.
In some embodiments, a characteristic dimension of the plurality of solder bumps may be selected based upon a representative focal distance between the one or more optical devices and the one or more optical lenses.
The one or more optical devices may include a vertical cavity surface emitting laser or a detector, or both.
In another aspect, the invention features an optoelectronic device comprising an optical lens system and an optical device system. The optical lens system includes a lens substrate supporting one or more optical lenses, and a spacer substrate defining one or more apertures therethrough. The optical device system includes a device substrate supporting one or more optical devices. The lens substrate is bonded to the spacer substrate and the spacer substrate is bonded to the device substrate with the one or more optical lenses, the one or more optical apertures and the one or more optical devices held together in registered alignment.
In another aspect, the invention features a method of aligning an optical device system and an optical lens system. In accordance with this inventive method, an optical device system having one or more of optical devices and a solderable metallization pattern is positioned adjacent to an optical lens system having one or more of optical lenses and a solderable metallization pattern with a plurality of solder bumps disposed thereon. The plurality of solder bumps are heated to a temperature at or above the melting point of the solder bumps. Upon cooling, the plurality of solder bumps bond the optical device system to the optical lens system with the one or more optical devices aligned with the one or more optical lenses.
Among the advantages of the invention are the following.
By enabling the optical device system to be passively aligned with the optical lens system, the invention reduces manufacturing costs and manufacturing time. The invention also reduces the sensitivity of the optical device performance to the thickness of the optical device substrate by bonding the device side of the optical device substrate to the device bonding surface of the optical lens system. In addition, the invention enables electrical connections to be made through the solder bump bonds and, thereby, avoids the need for wirebond electrical connections. This feature reduces inductance and electromagnetic interference (EMI) emissions commonly associated with such wirebond connections.